This invention relates generally to dishwashers and, more particularly, to dishwashers having a sanitation cycle feature.
A dishwashing machine typically includes a water pump, spinning water jets, and a controller for executing a number of different wash cycles according to user preference, such as that disclosed in U.S. Pat. No. 4,334,143. The cleaning efficacy achieved by domestic spray-type dishwashing machines in executing those wash cycles, however, is generally determined by the manufacturer""s of the machines. A public interest group known as the National Sanitation Foundation (N.S.F.) has promulgated minimum voluntary standards that have generally been accepted by dishwasher manufacturers, and that are increasingly desired by consumers. The current N.S.F. protocol (Protocol No. 95/480/05/2480) for the performance of domestic spray-type dishwashers requires that a dishwasher sanitation cycle has a time, temperature relationship that exposes dishwasher contents to a minimum amount of heat, measured in theoretical Heat Unit Equivalents (HUE).
However, the theoretical HUE construct is not always physically realized due to fluctuations in dishwasher system conditions, such as water temperature, during all or a portion of a dishwasher cycle. If water temperature drops, the dishwasher contents may not be sufficiently sanitized. If water temperature rises, dishes may be over-sanitized, which is energy inefficient. Consequently, the accuracy and energy efficiency of dishwasher sanitation cycles are often suspect.
Accordingly, it would be desirable to provide a dishwasher with an accurate sanitation cycle that minimizes the time and energy required to complete a desired degree of sanitization.
In an exemplary embodiment of the invention, a method for sanitizing the contents of a dishwasher including a rinse water temperature sensor, a rinse water heater, and a controller coupled to the sensor and to the water heater, includes determining the temperature of the rinse water at fixed time intervals with the sensor. The sensed temperature is supplied to the controller, which compares the determined temperature of the rinse water to a minimum sanitation cycle temperature, a low sanitation cycle temperature, and a high sanitation cycle temperature.
The minimum sanitation cycle temperature is the lowest temperature recognized by N.S.F. that has a tabulated HUE value. For each timer interval when the determined temperature is at least the minimum sanitation cycle temperature, an HUE value corresponding to the determined temperature is indexed from a memory of the controller. HUEs are cumulatively summed at successive intervals while the determined temperature equals or exceeds the minimum sanitation cycle temperature. The process is repeated with each successive time interval until the summed HUE total equals or exceeds a minimum value according to N.S.F. protocol.
The low and high sanitation cycle temperatures are used to execute a heating cycle for each time interval in response to the determined temperature. The low sanitation cycle temperature is predetermined to minimize sanitation cycle time while avoiding excessive hysteresis, i.e. cycling of the heater. The high sanitation cycle temperature is determined by the crazing of glassware and dishware placed in the dishwasher. When the determined temperature is less than the low sanitation cycle temperature, the water heater is turned on. When the determined temperature is greater than a high sanitation cycle temperature, the water heater is turned off. Thus, water temperature is optimized to minimize cycle time at energy-saving temperatures.
Thus, an accurate dishwasher sanitation cycle is provided that conserves energy and the required time to complete a sanitation cycle while ensuring that a minimum level of sanitation is achieved.